A conventional display device to display such as an image is described below. Until now, as the kind of display device, CRT (Cathode Ray Tube) was a main stream, however these years a liquid crystal display using an active matrix type of liquid crystal display panel (LCD) is widely pervaded. The LCD is not an emissive display, so it visualizes by utilizing transmission or reflection of outside lights or being in combination wit an illumination device (a device placed at back face of the liquid crystal display panel is called a backlight). Accordingly, although pixel displaying operation of the liquid crystal display panel is realized by a light transmittance control from the backlight, it is expressed for convenience as the “light emission” in explanation of display operation of the liquid crystal display below.
The liquid crystal display is a hold-type display different from the CRT which is an impulse-type display, so it is reported in pages 19 through 26 of technical document EID96-4 in Institute of Telecommunications Engineers and the like that an image quality is degraded when displaying motion pictures. According to such the documents, a blur occurs in motion picture images by disaccordance of eye movement due to motion picture images with hold light emission and human vision pursuit characteristics, thereby a motion picture quality being lowered In order to improve degradation of the motion picture quality, it is also described that there exists a method that a frame frequency (display frequency of one screen) is made n-fold rate, or image display is made 1/n fame period and a remaining period made to be displayed in blank. Meanwhile, here the larger a numeral value of the n, the more effective also for motion pictures moving at a higher rate.
A method to realize the improvement method of the motion picture quality, for example, as described in Japan patent laid open publication 2002-49037, generates light emission by concentrating lights only on a part of a backlight at which a light source unit with a linear light source at a side edge of a transparent light transmission sheet is placed, and scrolls the light emission portion being synchronized with a pixel scan of a liquid crystal display, thereby display being made 1/n period and quasi impulse display and a motion picture blur being alleviated. The light selective concentration type of backlight is not needed to flicker a light source, so a needed number of light sources can be lessened.
However, in the light selective concentration type of backlight in the method disclosed in “the above Japan patent”, all lights from the light source unit is not always emitted to the liquid crystal display panel side, so the light selective concentration type has a limit at a ratio of outgoing lights into the liquid crystal display panel from a light pipe for incident lights into the light pipe, that is, in a light utilizing efficiency. There exist two causes for this. One is that a scattering profile of a liquid crystal which should scatter lights in an outgoing direction at a selected portion is insufficient and lights are not effectively emitted in a direction of the liquid crystal display panel. The other is that the incident lights uniformly distribute in the light pipe, whereby lights not scattering at the selected portion exist. According to these, the light utilizing efficiency as the backlight results in lowering, thereby an advantage of the light selective concentration backlight which ought to reduce a number of light sources being nullified.